1. Field of the Invention
The present invention relates to a fluorescent screen of a color CRT and its fabricating method, and more particularly, to a fluorescent screen structure of a color CRT which is directed to improve contrast characteristics, luminance characteristics and color purity of a screen, and to a fluorescent screen of a color CRT and its fabricating method which is capable of simplifying a fabricating process of the fluorescent screen.
2. Description of the Background Art
Generally, a color CRT is an instrument in which an electronic beam radiated from an electric gun hits a fluorescent screen formed on the inner surface of a panel, to thereby implement a picture. Recently, as the screen is being enlarged in size, it requires more improved luminance characteristics and contrast characteristics, for which research is being done.
For example, in order to obtain favorable contrast characteristics, there has been proposed that using of a dark glass of which light transmittance is approximately 36%-55% as a panel, forming a fluorescent material layer by using a fluorescent with an inorganic pigment of the same color attached on the surface of the particles thereof, or forming a three-color filter layer having the same color as that of the fluorescent material layer between the three-colored fluorescent material layer and a panel where a black matrix is formed to thereby improve a selective permeability.
However, the three methods proposed for improvement of the contrast characteristics respectively include the following disadvantages.
First, in case of the fluorescent screen of a color CRT using the dark glass as a panel, though the contrast characteristics of the screen can be improved by absorbing an external light by means of the dark glass, since the dark glass also absorbs the light emitting of the fluorescent screen, the luminance characteristics of the screen is degraded.
Secondly, in case of the color CRT in which the fluorescent material layer is formed by using a fluorescent material with pigment attached, though the contrast characteristics is improved as the attached pigment absorbs the external light, since the fluorescent material particles are overlapped to various layers to form a fluorescent screen, the light emitting of the fluorescent screen is partially absorbed to the pigment, resulting in that the luminance characteristics of the screen is degraded. In addition, since the pigment prevents electron discharged from the electron beam from colliding with the core of the fluorescent material, the luminance characteristics are degraded.
In order to solve the problem, as shown in FIG. 1, there has been o proposed a fluorescent screen where 3 color filter layer is formed which corresponds to the three-color fluorescent material layer.
FIG. 1 shows a fluorescent screen of a color CRT in which three color filter layers are formed in accordance with a conventional an.
In the drawing, the fluorescent screen has a structure in that three-color filter layers (3R, 3G and 3B) are formed on a panel 1 on which a black matrix 2 was formed, and three color fluorescent material layers (4R, 4G and 4B) are formed corresponding to the three color filter layers (3R, 3G and 36).
There are various methods of forming the three color filter layers (3R, 3G and 3B), of which two representative methods will now be described.
One method:
A black matrix 2 is formed on the inner surface of the panel 1 of which light transmittance is approximately 70%-85% by a conventional method.
Sensitizing solution composed of polyvinyl alcohol PVA and ammonium dichromate ADC and a filter slurry liquid mixed with pigment dispersion liquid are coated and dried on the inner surface of the panel 1 where the black matrix 2.
The portions where each filter layer is to be formed is exposed by using a shadow mask. For example, in case of forming a green filter layer 3G, only the portion where the green filter layer 3G is to be formed is exposed to form a photoresist film, which is then developed by using water. And then, the other region except for a portion where the green filter layer 3G is to be formed is washed away, and only the green filter layer 3G remains. In order to form the red filter layer 3R or the blue filter layer 3B, the same process is repeatedly performed for the portions where each filter layer is to be formed.
Another method:
A black matrix 2 is formed on the inner surface of the panel 1 of which light transmittance is approximately 70%xcx9c85% by a conyentional method.
Sensitizing solution composed of polyvinyl alcohol PVA and ammonium dichromate ADC is coated and dried on the inner surface of the panel 1 where the black matrix 2.
The portion except for the region where the green filter layer 3G is to be formed is exposed and hardened to form a photoresist film, and then a green color pigment dispersion liquid is coated and dried on the inner surface of the panel where the photoresist film was formed.
The photoresist film is detached by etching process by using an etching solution such as aqueous hydrogen peroxide (H2O2) and developed by a strong hydraulic pressure. Then the photoresist film is removed and a green filter layer 3G is formed. In case of the red filter layer 3R and the blue filter layer 3B, the same process is repeatedly performed to thereby form filter layers.
After the three filter layers 3R, 3G and 3B are formed, on which fluorescent material layers 4R, 4G and 4B are formed corresponding to each filter layer, thereby completing a fluorescent screen structure of a color CRT having three color filter layers.
Reference numeral 5 of FIG. 1 denotes an aluminum film for preventing the electron beam from deviating backward and for rendering the light emitted in the backward direction to be reflected in the forward direction, and reference numeral 6 is a coloration film or a coloration coating layer for improving the contrast characteristics of the screen.
As mentioned above, in case that the three-color filter layers 3R, 3G and 3B are formed on the fluorescent screen of the color CRT, its contrast and luminance can be improved by 10%xcx9c20% compared to the color CRT using the fluorescent material attached by the pigment.
A Japanese Open Laid No. 9-27284 discloses that since the three-color filter layers 3R, 3G and 3B has the maximum transmittance for the light having a wave length in the range of approximate xc2x120 nm of the maximum light emitting wave length region of the three-color fluorescent material layers 4R, 4G and 4B corresponding to each filter layer and have relatively low transmittance for the other wave length region, the contrast characteristics of the color CRT can be improved.
Substantially, as shown in FIGS. 2A, 2B and 2C, the transmittance of each filter layer 3R, 3G and 3B for the light emitting region of the red, green and blue fluorescent material layers 4R, 4G and 4B is effective in the maximum light emitting region of each fluorescent material layer.
In case of the blue filter layer 3B, as shown in FIG. 2A, it has approximately 70% transmittance at 450 nm, that is, the maximum light emitting region of the blue fluorescent material layer 4B, while in case of the red filter layer 3R, as shown in FIG. 2B, it has approximately 60% transmittance at 625 nm, that is, the maximum light emitting region of the red fluorescent material layer 4R. Meanwhile, in case of the green filter layer 3G, as shown in FIG. 2C, it has approximately 70% transmittance at 530 nm, that is, the maximum light emitting region of the green forescent material layer 4G.
However, the conventional art has the following problems.
Though forming each filter layer for each fluorescent material layer is effective in the aspect of improving the contrast characteristics and the luminance characteristics of the color CRT, since the three filter layers need to be formed, the number of the processes is inevitably increased additionally and its productivity is degraded.
Also, equipments are required for forming each filter layer, causing an increase in the material cost which is led to an increased in a production cost.
In addition, due to the process spread according to the increase in the number of processes, the defective proportion of products is increased.
Therefore, an object of the present invention is to provide a fluorescent screen for a color CRT and its fabricating method which is capable of simplifying a structure of the fluorescent screen of the color CRT and its fabricating method.
Another object of the present invention is to provide a structure of a fluorescent screen of a color CRT and its fabricating method which is capable of improving contrast and luminance characteristics and color purity of a color CRT as well as simplifying its fabricating method without forming not all of three-color filter layers.
To achieve these and other advantages and in accordance with the purposed of the present invention, as embodied and broadly described herein, there is provided a fluorescent screen for a color CRT including a panel having a predetermined light transmittance; a black matrix formed on the inner surface of the panel for absorbing an external light; red, green and blue fluorescent material layers positioned on the upper surface of the panel where the black matrix is formed for emitting light corresponding to each color; a red filter layer positioned between the red fluorescent material layer and the panel, for absorbing light having wave length except for the main light emitting region of the red fluorescent material layer; and a blue filter layer positioned between the red fluorescent material layer and the panel and the green fluorescent material layer and the panel, for absorbing light having a wave length except for the main light emitting region of the green fluorescent material layer and the blue fluorescent material layer.
The blue filter layer has a more than 70% transmittance for a light having 450 nm wave length, that is, the main light emitting region of the blue fluorescent material layer, and has a more than 60% transmittance for a light having a 530 nm wave length, that is, the main light emitting region of the green fluorescent material layer.
Also, in order to achieve the above object, there is also provided a method for fabricating a fluorescent screen of a color CRT including the steps of: forming a black matrix, that is, an external light absorbing layer, on the upper surface of a panel having a predetermined light transmittance; coating a sensitizing solution on the upper surface of the panel where the black matrix was formed, exposing and hardening a green color portion and a blue color portion, and developing them with water to form a photoresist film; coating and drying a red color pigment dispersion liquid that a red color pigment is dispersed with water and a dispersion agent on the photoresist film, and detaching the photoresist film photosensitized with an etching solution, to form a red filter layer; coating and drying a blue color pigment dispersion liquid that a red color pigment is dispersed with water and a dispersion agent and a blue filter slurry liquid composing of a sensitizing solution on the inner surface of the panel, exposing and hardening a green portion and a blue portion, and developing them with water, to form a blue filter layer; and forming a red to fluorescent material layer on the upper surface of the red filter layer, and respectively forming a blue fluorescent material layer and a green fluorescent material layer on the upper surface of the blue filter layer positioned on the green and blue portions.
The red color pigment dispersion liquid contains ferric oxide (Fe2O3) with content of 5 wt %xcx9c20 wt %, and the blue color pigment dispersion liquid contains cobalt blue (CoOxe2x80x94Al2O3) with content of 5 wt %xcx9c25 wt %.